Typical automotive vehicle exhaust systems, and an increasing number of non-automotive applications utilizing internal combustion engines, have catalytic converters disposed in the exhaust system for reducing the quantity of regulated exhaust constituents emitted therefrom. A common converter configuration utilizes a catalyst coated ceramic substrate packaged within a stainless steel canister. Openings on either side of the substrate conduct exhaust gas into, through, and out of the converter. The substrate is typically extruded and has catalyst coated passages through which the exhaust gas passes as it transits the converter.
An alternative to the ceramic substrate converter is the metal foil converter which utilizes a stack or coil of catalyst coated, corrugated metal foil sheets which are held together mechanically or by bonding to form a substrate. The metal foil substrate is mounted within a canister in a manner similar to the ceramic substrate. Placement of the sheets in a face-to-face orientation defines fluid flow passages between the sheets through which exhaust gas may flow.
Typical application of the catalytic converters heretofore described place the assembly in an under-body location where space considerations determine converter and, consequently, substrate size. In a common converter configuration described in Hood U.S. Pat. No. 4,559,205 issued Dec. 17, 1985 and assigned to the assignee of the present invention, the substrate is constructed such that the inlet and outlet faces are substantially perpendicular to the flow channels passing therethrough. The substrate is disposed within a canister such that the plume of incoming exhaust gas flows through the entrance cone with little expansion until it encounters the restriction to flow imposed by the inlet face at which point a portion of the flow passes directly through the substrate while the remainder of the flow is diverted to flow parallel to the inlet face of the substrate. The parallel flowing exhaust gas spreads over the face until it is turned again to flow through outer channels of the substrate. Each directional change imposed on the exhaust gas flow, as it transits the converter, adds to the restriction imposed on the system by the converter assembly.
In order to increase catalytic treatment area, it has been necessary to place multiple substrates in series in a single canister. Multiple bed designs, as such designs may be referred to, while increasing catalyst treatment area, have the drawback of increasing backpressure imposed on the exhaust system since the restriction imposed on the exhaust system by a converter is a function of the flow length and the inlet area of the substrate. Multiple bed designs increase the flow length while maintaining a constant inlet face area.
To reduce the backpressure imposed on the exhaust system by the converter, it may be desirable to increase substrate inlet face area (frontal area) while decreasing overall flow length and limiting increases in converter cross-section. In the case of converters having angled inlets, the entrance is at an angle to the substrate inlet face allowing for improved flow conditions as the gas approaches the substrate and an increase in frontal area with minimum effect on the converter cross section. Flow efficiency continues to suffer however due to the directional change experienced by the exhaust gas since the incoming flow must turn through the angle established by the flow channels, relative to exhaust flow direction, which extend perpendicular to the inlet face of the substrate.